Insights on Adenomyosis Development

Adenomyosis is a gynecological condition defined as the presence of endometrial glands and stroma deep within the myometrium, causing myometrial hypertrophy, hyperplasia, and fibrosis. In the past, it was thought that adenomyosis affected almost exclusively multiparous women after 40 years, and the diagnosis was generally confirmed upon hysterectomy. Nowadays, by using imaging techniques such as transvaginal ultrasound (TVUS) and magnetic resonance imaging (MRI), adenomyosis is increasingly identified in young women with pain, abnormal uterine bleeding (AUB), and infertility or asymptomatic women. Although the pathogenesis of adenomyosis remains unclear, two main theories have been proposed: (a) invagination of the endometrial basalis into the myometrium and (b) metaplasia of displaced embryonic pluripotent Müllerian remnants or differentiation of adult stem cells. Key pathogenic mechanisms of adenomyosis include estrogen dependence, progesterone resistance, inflammation, aberrant immune responses, cell proliferation, migration, invasion, fibrosis, and neuroangiogenesis.